Existing dental equipment use various systems for controlling the delivery of fluid such as water or compressed air, utilizing means to pass or stop fluid flow as well as adjusting the level of fluid flow when passed through. Examples of such fluid delivery systems include, bowl rinse of water, water cup filler, flush of corrosive cleaning fluids through tubing parts, supply of air or liquid coolants to oral tools, etc. In such systems, fluid flow may be controlled by elastically manipulating a flexible tubing segment inserted in the fluid path, such as through a clamping, pinching, or folding (kinking) action to restrict or stop the flow.
As an example, U.S. Pat. No. 5,295,825 describes a control system for supplying fluids to a dental handpiece that includes a pinch valve having a flexible tubing passing the fluid supply. As with other systems using pinch valves, or clamp valves, fluid flow adjustments may not be adequately consistent for air and water due to inconsistent elastic recursion of the flexible tubing to its normal relaxed shape upon removal of the pinching action.
An example of a folding valve is that described in U.S. Pat. No. 3,395,838. There, the valve is connected at one end to a piece of tubing coming from an aerosol can, and at its opening makes direct contact with the fluid medium. Such a valve mechanism is not suitable for use in dental handpiece control equipment, as it only provides a single manual on-off control specifically dedicated for use with an aerosol can. In addition, the contact between the fluid medium and the valve itself presents other problems in dental equipment for reasons further explained below.
U.S. Pat. Nos. 5,407,351 and 5,425,634 describe an apparatus for controlling fluid delivery to a dental handpiece that includes a flexible tube valve arrangement inserted in series within the main fluid tubing via a pair of tubular fittings. Such a system requires the use of a fixed dedicated length of flex tube for its folding action. In addition, it requires two other extraneous valve arrangements for performing the fluid relay, flow adjustment and logic control functions. This makes the fluid flow system rather complicated to manufacture. Furthermore, in systems that employ seals as part of the various fittings, the seals may become contaminated thereby impeding fluid transfer. Another limitation is that the flow control valve is normally open with the risk of accidental flow of fluid upon inadvertent interruption in the pressurized pneumatic air supply for regulating the flow of fluid.
In dental equipment, the fluid delivery system is regularly cleaned by flushing the fluid path with mildly corrosive or antibacterial cleaning chemicals, such as chlorhexidine, bleach or ozone. Such chemicals may gradually corrode or contaminate metal, rubber and other corrosive non-resistant parts along the fluid path in the tubing. The more parts used on the fluid path, the greater is the risk of corrosive damage.
In view of the limitations in the prior art reviewed above, there is clearly an important need for economical fluid flow control systems that avoid any potential corrosive damage to metal valve bodies or rubber seals associated with the fluid path, by minimizing, or avoiding altogether, the utilization of such elements.